Ian Rutledge is sent to investigate the murder of the youngish Colonel Harris. The murder is a bit tricky because unfortunately, the only suspect seems to be a young, dashing war hero, Captain Mark Wilton, who is engaged to the colonel's ward, Lettice (also, is it pronounced like lettuce or like that eyelash drug, Latisse?). More unfortunately, the only witness who could place Captain Wilton near the murder is a shell-shocked man who has spiraled into alcoholism. Not only will no one believe the word of a drunk shirker (in the opinion of the locals) over the word of a decorated hero who is friends with the Prince of Wales, but Inspector Rutledge himself suffers from PTSD and is very keen to keep it a secret.
Everyone is suspect of course -- Charles Harris and Mark Wilton were seen by the servants bitterly fighting the night before the murder, presumably about the wedding; Mark's former flame, the artist Catherine Tarrent is still bitter over the demise of her German lover during the war; Mavers is a troublemaker who detests basically everyone, but is secretly receiving a pension from Charles; Lettice was angry with Charles for cancelling her wedding and was seen arguing with him outside the inn; Mark's cousin may or may not be in love with him.
Eventually, we find out that Charles did call off the wedding, but not against Lettice's wishes: Lettice and Charles were in love and finally admitted it to one another. Meanwhile, the true murderer was the deranged Helena / Maggie, who killed Charles after mistakenly believing he ran over and killed a child in his youth. I can't even.
Meanwhile, back at the police headquarters, Superintendent Bowles laments, in the manner of Dr. Claw, that his nefarious plan to get rid of Rutledge didn't work but then muses that there is always next time. Seriously, do people truly scheme like this in real life? I must know and befriend them.